Belt and gear drive



Oct. 3, 1961 A. L. WORRALL, JR

BELT AND GEAR DRIVE 2 Sheets-Sheet 1 Filed April 27, 1959 A TT OENEY1961 A. L. WORRALL, JR

BELT AND GEAR DRIVE 2 Sheets-Sheet 2 Filed April 27, 1959 INVENTOR.AJHIW/V .M/P/PALL, 6/):

m Q rmm ATTORNEY BELT AND GEAR DRIVE Ashton 'L. Worrall, .lr., CuyahogaFalls, Ohio, assignor to United States Rubber Company, New York, N.Y., a

corporation of New .lersey Filed Apr. 27, 1959, Ser. No. 809,283 3Claims. (Q1. '74-229) This application is a continuation-in-part of mycopending applications Serial Nos. 698,112, new Patent Number 2,934,967,and 734,286, now Patent Number 2,937,538. This invention relates to ahigh power positive drive comprising the combination of a flexible beltand gears in which the gears are provided with teeth having involutefaces which mesh with teeth on a belt with reduced interference, theteeth of the belt also having involute working faces.

The power drive embodying this invention is particularly useful for thepositive transmission of power at relatively high levels between two ormore gears and finds its particular importance in providing the basictransmission mechanism in an automobile, the basic automotive drivesystem, and may be used in place of the cur- .rent direct coupled shaftsystems.

' One object of this invention is to obtain continuous action and toreduce interference between the teeth of the belt and of the gears in ahigh power transmitting application.

, A further object of this invention is to reduce the noise andvibration resulting from the engagement and disengagement of the beltand gear teeth in high power appli- "cations.

' This invention is further described in reference to the accompanyingdrawings in which:

FIG. 1 is an elevational view of a positive power drive embodying thisinvention;

FIG. 2 is an elevational view of a portion of the belt and the smallestgear of the power drive showing the construction of the belt teeth inreference to a straight faced 'gear tooth; and

FIG. 3 is an enlarged side elevation of a portion of the belt having aninvolute tooth profile which meshes with a gear having an involutegroove profile and represents the preferred embodiment of thisinvention. 7

The method of making each of the components of this power drive, namelythe belt and the gear, may best be explained by referring to myco-pending applications. The construction of the belt and gear dependsupon the selection of the pitch circle of the smallest pulley used inthe power drive. Once the pitch circle of the smallest pulley isselected, then assuming belt teeth are straight faced, involute beltteeth are developed as explained in Serial No. 734,286. That is theconjugate involute toothed belt is developed from the straight facedtoothed belt that satisfies the pitch diameter of the smallest pulley.

Summarizing the procedure thus far, the pitch circle of the smallestpulley to be used is determined and on the basis of this pitch circle, astraight faced toothed belt is laid out; from this straight facedtoothed belt, it is then possible to develop the conjugate belt'thatwill satisfy the pitch diameter of the smallest pulley. This conjugatebelt will have an involute tooth profile as described in the aforesaidapplication.

Having therefore derived an involute profiled toothed belt from astraight faced toothed belt, it is then possible to develop an involuteprofiled pulley, on the basis of the straight faced toothed beltdescribed in Serial No. 698,112.

Summarizing again, step number 1 is to determine the pitch circle of thesmallest pulley. Step number 2 is to decide on the straight facedtoothed belt. This belt does mot have involute profiled teeth. Stepnumber 3 is to .-develop the conjugate form of the straight facedtoothed belt from the belt obtained at step 2 to satisfy the pitch ratesatent diameter of the smallest pulley as determined at step 1. Thus far,from step 2 the conjugate belt has been derived having the involuteprofiled teeth. Step number 4 is to develop an involute profiled pulleyfrom the belt obtained at step number 2.

This procedure will be explained in further detail by referring to thedrawings.

As shown in FIG. 1, the power drive comprises a toothed belt 10 whichtransmits motion between gears 11 and 12 either of which may be thedriving gear. The belt 10 is provided with teeth 13, which mesh withgear teeth 14 and 15. Means are provided for keeping the belt 10 undergears, and for that purpose as shown herein, flanges 16 are provided forthe smaller gear. Except for the contour of the belt teeth face and ofthe gear teeth face, the belt 10 may be constructed as shown anddescribed in United States Patent No. 2,507,852 to Richard Y. Case andmay be an endless flexible plastic or rubber belt having teeth formedthereon or bonded thereto. As shown in FIG. 2 of the drawings herein,the belt 10 is provided with a load carrying or pull member 17, thecenter of which forms the neutral axis, or pitch line 18 of the belt.The inside, or tooth side of the belt, and the teeth thereon are coveredwith a fabric jacket 19, however a jacket is not essential. The exposedsurface of the jacket forms the dedendum line 20 of the belt teeth 13,and when the belt goes around the gears the dedendum line 20 coincideswith the addendum circle 21 of the gear.

The belt and gears of the power drive have the followingcharacteristics, which are described in reference to gear 11. The pitch22 of the belt teeth 13 as measured on the pitch line 18 is equal to thepitch of the gear teeth 14 and 15 as measured on their pitch circle, ofwhich pitch circle 23 of gear 11 is representative as shown in FIG. 2.The pressure angle 24 of the belt and gear teeth is measured between aradial line 25 of any gear and pressure angle line 26, which coincideswith the straight faces 27 of gear teeth 14. Gear faces 27 are tangentto involute curves 28 which form the convex face profile of the beltteeth 13. The distance 30 between the pitch line of the belt and thededendum line 20 is equal to the distance 31 between the pitch circle 23and the addendum circle 21. Such distances 30 and 31 are referred to asa pitch differential, and should be as small as practical.

Having selected the above mentioned characteristic, the smallest gearupon which the belt is adapted to operate is chosen and the constructionof the belt teeth is then determined for conjugate operation asdescribed hereinafter.

A portion of gear 11, the smallest gear that belt 10 is adapted tooperate with, is shown at FIG. 2 having teeth 14 and a groove 32therebetween. It is to be noted the gear shown is only diagrammatic,required only to form the belt and is not the actual gear used to drivebelt 10. This gear is laid out as follows. Pitch circle 23 of gear 11 isdrawn about a center 33 with a radius 34 to provide a pitch circlehaving a predetermined number of equally spaced grooves 32. The addendumcircle is laid out with the radius 35 equal to the radius 34 of thepitch circle 23 less the pitch differential 31. The dedendum circle 36is laid out with the radius 37 equal to the radius 35 of the addendumcircle 21 less the working depth 88 of the gear teeth 14. A tangent 39is drawn to the dedendum circle 36 at its intersection 40 with theradius 25, which passes through the center of the groove 32. One-half ofthe bottom width 41 of the groove 32. is laid out on the line 39 on eachside of the intersection 40 to establish the corner points 42 and 43 ofthe groove. The angle lines 26 are then drawn through the radial points42 and 43 at the angle 24 to the radial line 25. The extension of thelines 26 between dedendum circle 36 and the addendum circle 21 forms 1angle.

3 the straight sides or plane faces 27 of gear teeth id. The top andbottom of the faces 27 are rounded with arcs as and 45 of suitableradii.

After gear 1 1' is diagrammatically laid out theprofile of the beltteeth may be constructed as follows. Having extended the radius 25 ofthe gear ll perpendicrlar to the pitch line 18 of the belt to. form thepitch point as, the tooth pressure or action lines 47 and 48 are drawnthrough the pitch point as at an angle 49 to the pitch line 18 or" thebelt lll equal to the pressure angle 2.4. The base circle: is. drawn.from a center not shown on the radial line: 25: outside of the pitchcircle 23 of the gear 11:, and; with. the. radius equal in radius 3 4 ofpitch circle 23. Action. lines 47 and are tangent to thecircl'e- 51 Theinvolute curves 28 are derived from base. circle: as and are tangent tothe pressure angle lines- 26 at the. intersections 51 of the lines aswith the lines 47 and. 4-8;. lines 26 are perpendicular to the lines 47and 48. The working. faces 2? of the belt teeth 13 are. formed by thatportion. of the involute curves 2%, which extend beyond. the dedendamline 23b of the belt tothe dedendnm circle as of the gear, exclusive ofarcs; 52 and 53. of. suitable radii located at the bottom and top of:the; teeth.

As described herein, no clearance is provided between the belt teeth andthe gear teeth. Suitable clearance maybe providedin accordance withconventional prac rice. It is to be noted that it is only necessary tocon sider the design of the teeth of the belt as fiat or 'raight in.order to design. the gear and in the embodiment of this invention, thebelt teeth are involute. The belt that is used to determine the. gearteeth is the fiat or straight toothed belt from which the. involutetoothed belt sun face has. also been derived. Having laid out the beltas described heretofore, the gear 140, shown at FIG. 3 is constructed tocooperate with the. belt by first selectiug pitch circle do of the gearso that the pitch line 115 of the belt isv tangent to it. The. pitch ofthe gear teeth must be the sauce as the pitch 2?. of the belt teeth, andsuch pitch is laid out on. the pitch circle so between the pitch centersas of the grooves between teeth 13a. The addendum 27d of the belt teethis equal to the dedendum: 61 of. the gear teeth, which latter is laidout along; the radius 62. of the gear inwardly from the pitch point asof. the gear groove to form a point on the dedendum circle 64 of thegear Mu. It will be noted under these conditions the. belt teeth are alladdendum and the cooperating gear teeth are all dedendnrn. A tangent 65to the dedendurn circle dd is drawn through point 63.

Now the angular outline of the belt tooth is drawn in the gear groove.To do so, the gear radius becomes the center line of the belt tooth andthe tangent es becomes the addendum line of such tooth. One halt of thewidth of the belt tooth is laid out along the tangent 65 from the point63 to establish the corner .e a of the tooth. A line as is. then drawnthrough the point 29w at an angle 24 to a perpendicular 6'7 to thetangent 65 representing the face 72 of the belt tooth. A line 6-8 is.drawn through the pitch point at center of the gear. groove so that thepressure angle 24 is included between the line i3 and a tangent 65 tothe pitch circle 8d. at the pitch point as. The line will beperpendicular to line 66 andv tangent to the base circle fit which isconcentric to the pitch circle so.

The base circle '76} may be also determined by computing its diameter,which is equal to the diameter of the pitch circle multiplied by thecosine of the pressure Having determined its diameter, the base circlemay be drawn concentric to the pitch circle $9. in such case a tangentto the base circle thus drawn and passing through the pitch point 61)will coincide with line no.

The line 63 intersects the line 66 (representing the face of a belttooth) at the point '71, which establishes a point on the involuteprofiled face of the gear tooth.

- The contour of the involute profiled face "72 of the gear tooth is.formed by plotting the path of the POifll 7i under the condition that itis on a flexible member such as a string, attached to the base circle 7%at the point of tangency of the line 62; to the circle, and the stringis Wound counterclockwise under. tension around the circle 7% until thepath 75 of the point 71 intersects the dedendum circle The involuteprofiled face 74 for the other side oi the tooth is determined in thesame --cr as the face 72,

excepting after locating the point is corresponding tothe point 71, theinvolute profile face 7'2 is. determined by tracing the path of thepoint '75 on a flexible member tangent to the base. circle '76 whenwound clockwise around the circle. The opposite faces of all the gear"teet i may be determined in the same manner.

As shown and described herein no clearance is, pr vided in the gearteeth grooves for the belt teeth but. suitable clearance should beprovided to compensate for manufacturing inaccuracies.

Having laid out the belt and gear drive as described herein, thoseskilled in the art may produce the belt and gear by Well knownconventional methods of molding; and gear cutting.

The preferred. form of this invention has been. de: scribed herein, butchanges may be made therein without departing from the spirit of theinvention, and it is. in} tended to cover all such changes comingwithin. the scope of the appended claims and such changes as. may occurto those skilled in the art.

Having thus described my invention, what 1 claim and desire to protectby Letters Patent is:

l. A. high power positive drive comprising a flexible toothed. belt andgears therefor having teeth on their peripheries adapted to mesh withsaid belt, said belt teeth. and gear teeth having working faces of aninvolute contour and predetermined pressure angle, the pitch circles forsaid gears lying respectively outside the tops of said gear, theinvolute profile for the teeth of each. gear being derived from a basecircle having a diameter determined by multiplying its pitch circlediameter by the cosine of the pressure angle, the involute profile forsaid belt teeth being derived from a base circle having a diameterdetermined by multiplying the pitch circle diameter of: the smallestgear by the cosine of the pressure angle.

2. In. combination, an endless flexible toothed belt, the contour of theteeth thereon being involute, and gears therefor adapted to drive am bedriven by said belt, said gears having peripheral teeth of in olutecolltour.

3. A high power positive drive comprising a flexible toothed belt havinga tension member located substantiallyat the neutral axis, gearstherefor having teeth on their peripheries and being adapted to meshwith. said belt, said belt teeth and the gear teeth of at least one gearhaving working faces or an involute contour and predetermined pressureangle, the pitch circles for said gears lying respectively outside thetops of said gears, said neutral axis coinciding with said pitch circleswhere said axis curves around said gears, the involute profile for theteeth of each gear being derived from a base circle having a diameterdetermined by mul iplying its pitch circle diameter by the cosine of thepressure angle, the involuteprofile for belt teeth being derived from abase circle having a diameter determined by multiplying the pitch circlediameter of the smallest gear by the cosine of the pressure angle.

References Cited in the his or" this patent UNITED STATES PAT Case May10, I950 @THER REFERENCES The Involute' Gear, published by The Fellows.Gear Shaper Co., Springfield, Vermont (copyright 1920), pages relied on19, 20,- 33 and 34.

